A Wolf in Sheep's Clothing

The phrase Wolf In Sheep's Clothing pertains to a character who uses a false identity to conceal either his true identity, feelings, or motives. Characters that are "wolves in sheeps' clothing" might not necessarily be evil or intend malice, but they often are a cause of discomfort or distrust at the least.

From the Other Wiki: The phrase originates in a sermon by Jesus recorded in the Christian Bible: Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves (Gospel of Matthew, 7:15—King James Version). The sermon then suggests that their true nature will be revealed by their actions (by their fruits shall ye know them, verse 16).

Subverted in the Darkest Powers series by Derek Souza. He's standoffish and can be utterly tactless at times, but he's also a genuinely good person who still carries the guilt of the one time he accidentally hurt someone in self-defense. However everyone, including a family friend who's known him from childhood, assumes he's a violent thug pretending to be harmless. The humans fear him because he's over six feet tall and 220 pounds of solid muscle at the age of 16, and the supernaturals fear him because he's a werewolf. In short: Derek is usually assumed to be a wolf in sheep's clothing when, metaphorically, the opposite is true.

One short story includes the budding romance between two werewolves; one of them worries that the other may be "a sheep in wolves' clothing".

A Song of Ice and Fire, (being an entire series worth of Doorstopper sized Gambit Pileups), has no shortage of these, but one character who stands out for this trope is Petyr "Littlefinger" Baelish. He's an interesting example because he doesn't pretend to be nice (his affable persona is a deliberately Paper-Thin Disguise); the real pretence is that he acts like a Smug Snake when he is in fact a full-fledged Magnificent Bastard, so still fits the bill of pretending to be much less dangerous that he really is.

The Aesop fable of the hungry wolf that finds a sheep's fleece on the ground and adorned himself with it in order to sneak into the flock and steal sheep without being noticed. The wolf was later killed when the shepherd went looking for a sheep to slaughter for his own dinner and mistook the wolf for a sheep, although some versions have the wolf howling out in an attempt to imitate a sheep's bleating and being caught that way.

Played with in multiple fashions in Kevin and Kell, particularly in the relationship between Corrie (a sheep [1]) and Bruno (a wolf). Corrie spent a period as a sheep in wolf's clothing, since Bruno's best friend Rudy was opposed to carnivore/herbivore relationships.

Juvenile piranhas insinuate themselves into schools of other fishes, finding safety from larger predators in the crowd. They also feed off their non-piranha schoolmates, biting off pieces of the fins of unsuspecting companions.

Some types of livestock-guarding dog, such as the Great Pyrenees or Kuvasz, have been bred to look like sheep so they won't scare the herds they're supposed to be protecting.

In the United States Air Force, there is an entire Fighter Wing that earned its nickname from an operation based on this concept. During The Vietnam War, North Vietnamese MiGs were pouncing on American F-100 Super Sabres, older, clumsier fighters that had been relegated to doing bombing missions. The 8th Tactical Fighter Wing, under the leadership of Robin"The Wolf"Olds, launched an operation where F-4 Phantoms would fly the same routes as the F-100s, flying close together so that two Phantoms would resemble a single Super Sabre on the North Vietnamese pilots' radar. When the unwary North Vietnamese pilots closed to engage what they thought were vulnerable bombers, they realized, often too late, that they had blundered into an ambush. Ever since then, the 8th TFW (now simply known as the 8th Fighter Wing) has been called "The Wolfpack."

Q-ships are another example of this concept, merchant vessels with a disguised armament intended to lure enemy submarines into attacking them while surfaced. The flip side and more literal version of this is a merchant raider, a similarly fitted warship that attacks shipping. Both of these systems were used by the British and Germans respectively during World War I